1. Field of the Invention
The present invention relates to a base station apparatus, and in particular, to a base station apparatus capable of cooperating with another base station apparatus.
2. Description of the Related Art
Conventionally, there are communication systems, such as ETC (Electronic Toll Collection System) and a cellular system of a mobile phone, in which a plurality of base station apparatuses, each managing a predetermined zone, disposed at regular interval of distance perform narrowband communications using a DSRC (Dedicated Short Range Communication) method with a wireless communication apparatus that moves from zone to zone.
For example, Japanese Laid-open Patent Publication No. 2002-271258 discloses a communication system in which a base station apparatus performs wireless communications with a vehicle having a wireless communication apparatus (in-vehicle apparatus). Specifically, in the disclosed communication system, a plurality of base station apparatuses each managing a predetermined zone are disposed at regular interval of distance, a vehicle moves from zone to zone, and a center apparatus gives instructions of data transmission or the like to the plurality of base station apparatuses. The data is transmitted from the center apparatus to the vehicles via the base station apparatuses.
For example, data such as data on a traffic accident or guide data of service areas is transferred to a vehicle moving on a highway via the base station apparatuses disposed every highway interchange or every 100 meters on road shoulders of the highway.
The above-mentioned conventional art has a problem that communications between the base station apparatus and the in-vehicle apparatus are not performed reliably and smoothly without iteration.
FIGS. 16A to 18C are diagrams for illustrating a base station apparatus according to a conventional art. Examples will be described with reference to FIGS. 16A to 18C. A base station apparatus 10A according to the conventional art receives from a center apparatus 30, through a wired system, common data (e.g., data on a traffic accident) which is data to be transmitted to all in-vehicle apparatuses in a certain area. The base station apparatus 10A transmits the common data to the in-vehicle apparatuses in all vehicles indiscriminatingly within a zone managed by the base station apparatus 10A, that is, where wireless communications with the base station apparatus 10A can be performed, through wireless communication via radio waves or the like. In this case, the base station apparatus 10A does not receive responses to the common data from the in-vehicle apparatuses and does not detect statuses of apprise of the common data to the in-vehicle apparatuses (hereinafter, such an indiscriminating transmission of data from the base station apparatus is referred to as “broadcast apprise”).
Upon receiving a signal indicating a demand for certain data, the base station apparatus 10A according to the conventional art requests, to the center apparatus 30, the demanded data (e.g., data on a service area) to be provided in response to the signal. Upon receiving the demanded data, the base station apparatus specifies a pertinent in-vehicle apparatus, and transmits the demanded data to the specified in-vehicle apparatus individually. In this case, the base station apparatus receives a response to the demanded data from the in-vehicle apparatus, thereby detecting the status of apprise of the demanded data to the in-vehicle apparatus (hereinafter, such an individual transmission of demanded data to a specified in-vehicle apparatus from the base station apparatus is referred to as “individual apprise”).
On this assumption, when common data is distributed from the center apparatus to a plurality of base station apparatuses and broadcast apprised from the plurality of base station apparatuses, the base station apparatus according to the conventional art iteratively transmits the common data to the same in-vehicle apparatus. For example, as shown in FIGS. 16A and 16B, when data titled “COMMON X” is broadcast apprised from a plurality of base station apparatuses, the base station apparatuses (e.g., base station apparatus 10A and base station apparatus 10B) receive the data titled “COMMON X” from the center apparatus 30 (step S61). The base station apparatus 10A performs the broadcast apprise of the data titled “COMMON X” to in-vehicle apparatuses (e.g., in-vehicle apparatus 40) within a zone 20A managed by the base station apparatus 10A (step S62). Thereafter, a vehicle having the in-vehicle apparatus 40 moves to a zone 20B managed by the base station apparatus 10B. The base station apparatus 10B does not detect the status of apprise of the common data to the in-vehicle apparatus 40, and performs the broadcast apprise of the data titled “COMMON X” to the in-vehicle apparatuses (e.g., in-vehicle apparatus 40) within a zone 20B, similarly to the base station apparatus 10A (step S63). That is, the in-vehicle apparatus 40 iteratively receives the data titled “COMMON X”.
When common data is distributed to a specific base station apparatus from the center apparatus and broadcast apprised from the specific base station apparatus, the base station apparatus according to the conventional art does not reliably transmit the common data to in-vehicle apparatuses. For example, as shown in FIGS. 17A and 17B, when data titled “COMMON X” is broadcast apprised only from a specific base station apparatus (e.g., base station apparatus 10A), the base station apparatus 10A receives the data titled “COMMON X” from the center apparatus 30 (step S71), and performs the broadcast apprise of the data titled “COMMON X” to in-vehicle apparatuses (e.g., in-vehicle apparatus 40) within a zone 20A managed by the base station apparatus 10A (step S72). Herein, suppose that the in-vehicle apparatus 40 does not receive the data titled “COMMON X” from the base station apparatus 10A due to a radio disturbance or the like (step S73). Thereafter, a vehicle having the in-vehicle apparatus 40 moves to a zone 20B managed by the base station apparatus 10B. The base station apparatus 10A performs the broadcast apprise of the data titled “COMMON X” but the in-vehicle apparatus 40 is not within the zone 20A (step S74). The base station apparatus 10B does not receive the data titled “COMMON X” and does not perform the broadcast apprise of the data titled “COMMON X” (step S75). That is, the in-vehicle apparatus 40 cannot receive reliably the data titled “COMMON X” which should be received.
When demanded data is individually apprised, the base station apparatuses according to the conventional art individually receive a signal indicating a demand for data. Specifically, as shown in FIGS. 18A to 18C, a base station apparatus 10A receives a signal indicating a demand for data titled “DEMANDED Y” from an in-vehicle apparatus 40 (step S81). Then, the base station apparatus 10A requests the data to the center apparatus 30 (step S82), and only the base station apparatus 10A receives the data (step S83). If the in-vehicle apparatus 40 moves to a zone 20B from a zone 20A during this, the in-vehicle apparatus 40 is not within the zone 20A when the base station apparatus 10A attempts to transmit the data (step S84). The base station apparatus 10B does not receive the data titled “DEMANDED Y” and does not transmit the data (step S85). That is, the in-vehicle apparatus 40 cannot receive the data titled “DEMANDED Y”. Then, the in-vehicle apparatus 40 transmits again the signal indicating a demand for data titled “DEMANDED Y” and the base station apparatus 10B receives the signal (step S86). That is, the in-vehicle apparatus 40 iteratively transmits the same signal indicating the demand for data titled “DEMANDED Y” to the base station apparatus 10A and the base station apparatus 10B.
As mentioned above, the conventional art has a problem that the communications between the base station apparatus and the in-vehicle apparatus are not performed reliably and smoothly without iteration. In other words, the in-vehicle apparatus iteratively receives data that has been already received, does not reliably receive data, or iteratively demands for data.